Showing 5 results for A. Allahverdi
A. Allahverdi, E. Najafi Kani, S. Esmaeilpoor,
Volume 5, Issue 2 (spring 2008 2008)
Abstract
Abstract: The use of alkali-activated cementitious materials especially over the past decades has
significantly been increased. The goal of this research is to investigate the effects of silica modulus
and alkali concentration on alkali-activation of blast-furnace slag. In this research, the most
important physical characteristics of cementitious systems, i.e. the 28-day compressive strength
and final setting time, were studied by changing influencing parameters such as silica modulus,
i.e. SiO2/Na2O, (0.44, 0.52, 0.60, and 0.68) and Na2O concentration (4, 6, 8 and 10% by weight of
dry binder) at a constant water-to-dry binder ratio of 0.25. Final setting time of the studied
systems varies in the range between 55-386 minutes. The obtained results show that systems cured
at an atmosphere of more than 95% relative humidity at room temperature exhibit relatively high
28-day compressive strengths up to 107 MPa.
A. Allahverdi, E. Najafi Kani,
Volume 6, Issue 2 (Spring 2009 2009)
Abstract
geopolymer cement (inorganic polymeric binder) based on natural pozzolan are investigated. SiO
of activator and total molar ratios of Nacomposition exhibiting the highest 28-day compressive strength. Mixtures exhibiting the highest compressive strength were studied for their molecular structure using laboratory technique of Fourier transform infrared spectroscopy.Results obtained confirm that changes in chemical composition and curing condition can result in variations in degree of silicon substitution by aluminum in the second coordination sphere. Hydrothermal curing affects the molecular structure so that by increasing the hydrothermal curing temperatures, a lower degree of silicon substitution by aluminum in the second coordination sphere is observed. The molecular structure of the studied inorganic polymeric binde is composed of Si-O-Si chains bonded to Al-O and Si-O units creating two and three dimensional networks.
In this paper, the effects of chemical composition and curing conditions on molecular structure of2/Na2O molar ratio2O/Al2O3, and H2O/Al2O3 were changed to determine the optimum chemical
A. Allahverdi,, K. Kianpur, M. R. Moghbeli,
Volume 7, Issue 1 (winter 2010 2010)
Abstract
Abstract:
This work was designed to investigate the simultaneous effect of both water-to-cement (W/C) and polymer-to-cement
(P/C) ratios on flexural strength of type V Portland cement pastes containing polyvinyl alcohol. The obtained results
confirmed the strong effect of W/C-ratio on the effectiveness of the added polymer so that there exist optimum values
for both W/C and P/C-ratios. Pastes prepared at optimum W/C and P/C-ratios of respectively 0.30 and 0.016 exhibited
the highest flexural strength which was more than two times the strength of unmodified pastes. Further measurements
on hardened paste specimens prepared at W/C=0.30 show that increasing the P/C-ratio increases dry bulk specific
gravity of the specimens and result in significant reductions in both total permeable pore volume and water absorption
of the specimens confirming the effective packing caused by polyvinyl alcohol acetate.
Some water-soluble polymers have proved potentials for improvement in properties of Portland cements.
E. Najafi Kani, A. Allahverdi,
Volume 8, Issue 3 (september 2011 2011)
Abstract
Shrinkage behavior of a geopolymer cement paste prepared from pumice-type natural pozzolan was studied
by changing parameters of chemical composition including SiO2/Na2O molar ratio of activator and total molar ratios
of Na2O/Al2O3, and H2O/Al2O3. For investigating the effect of curing conditions on shrinkage, hydrothermal curing
was also applied. The obtained results clearly revealed the governing effect of chemical composition on shrinkage.
Mixes with different Na2O/Al2O3 molar ratios exhibited different shrinkage behavior due to variations made in
SiO2/Na2O molar ratio. Application of hydrothermal curing after a 7-day period of precuring in humid atmosphere
also showed strong effect on shrinkage reduction.
A. Allahverdi, E. Najafi Kani, M. Fazlinejhad,
Volume 8, Issue 4 (december 2011)
Abstract
Abstract: The linear expansion, early-age compressive strength and setting times of the binary mixtures of gypsum and Portland cement clinkers of relatively low C3A-contents were investigated. For this reason, type 1, 2, and 5 of Portland cement-clinkers were selected and a number of binary mixtures were designed. At relatively lower percentages of gypsum (about 5%), the early strength behavior is improved. Results obtained for compressive strength of mixtures with 5% gypsum confirm the possibility of achieving 28- and 90-day compressive strengths up to values higher than 100 MPa and 130 MPa, respectively. At relatively higher percentages of gypsum (more than 25%), excessive expansion caused by ettringite formation results in the formation of micro-cracks effectively weakening the strength behavior. The work suggests that type S expansive cements could be produced from Portland cement clinkers of relatively low C3Acontents.
